Along with the tendency towards ever more binding environmental laws, exhaust gas aftertreatment systems, which make possible the filtration or elimination of soot particles existing in combustion exhaust gases, are increasingly attaining importance. In order to check or to monitor the reliability of such exhaust gas aftertreatment systems, sensors are required by the use of which, even in the long run, an accurate ascertainment can be made of the instantaneous particle concentration present in the combustion exhaust gas. In addition, by the use of such sensors, it should become possible to make a prognosis of the degree of saturation of a Diesel particulate filter provided in an exhaust gas system, in order to attain a high degree of system safety and thereby be able to use more cost-effective filter materials.
A sensor is described in U.S. Pat. No. 6,634,210 for detecting substances in a fluid flow, which is developed on the basis of a ceramic multi-layer substrate. It includes two measuring electrodes, at a distance from each other, which are exposed to the combustion exhaust gas that is to be tested. If soot deposits between the two measuring electrodes, this produces a current flow between the measuring electrodes in response to the application of a voltage to the measuring electrodes. A heating element, designed in the form of layers, makes it possible to free the electrodes and their surroundings from deposited soot particles by way of a thermal process. The sensor also includes a temperature measurement element by which the temperature of the sensor can be detected. The temperature measurement element is located within the laminar structure of the sensor, between the heating element and the measuring electrodes. What is disadvantageous in this construction of the sensor is that the temperature ascertained via the temperature measurement element does not correspond to that temperature which prevails in the region of the measuring electrodes.
It is an object of the present invention to provide a sensor element for sensors, and a method for determining the concentration of particles in gas mixtures which permits an accurate temperature regulation and yet can be carried out in a cost-effective manner.